The present invention relates to a method and a device for quick pressure relief in a system having at least a first and a second housing part, it being the case that in the normal state the first housing part contains a hydrogen atmosphere at overpressure which is separated from the interior of the second housing part by a hydrogen seal, the overpressure of hydrogen being lowered via a quick discharge line upon failure of the hydrogen seal. The main field of application of the invention, to which it is not, however, limited, are hydrogen-cooled generators whose shafts are guided through various seals and housing parts, it being necessary to ensure the secure inclusion in the generator housing of the hydrogen at overpressure. In the case of leaks of hydrogen, the highly explosive oxyhydrogen gas can form in combination with air, which is to be prevented under all circumstances, even in the event of stoppages.
In a typical hydrogen-cooled generator according to the prior art, for example GB Patent 760,781 or the article entitled "A Study on Thermal Behavior of Large Seal-Ring" by T. Suganami, T. Masuda, N. Oishi and T. Shimazu in Journal of Lubrication Technology, October 1982, VOL 104/449, the generator shaft is guided through a labyrinth seal into a prechamber, then through a hydrogen seal into a so-called bearing compartment and from there to the outside into the machine hall or, for example to a turbine or a gear unit. It is likewise customary to effect the seal between the bearing compartment and machine hall by a labyrinth seal. Labyrinth seals are not completely gas-tight, but act only like a strong throttle valve, with the result that hydrogen can escape along these seals. In the normal state, the same pressure therefore prevails in the prechamber as in the generator housing. By contrast, essentially normal room air is located in the bearing compartment, which is closed with respect to the prechamber with a virtually complete sealing function by a hydrogen seal. Said air is held by means of a bleed pump at a slight underpressure so that any small quantities of hydrogen which do pass through the hydrogen seal cannot pass through the labyrinth seal of the bearing compartment into the machine hall, but are exhausted and released into the open.
In the case of failure of the hydrogen seal, it is known from WO 94/10739 A1 to open a quick discharge line through which the overpressure in the prechamber can be very quickly relieved. However, such a large volume is involved that it is possible, at least for a certain time, for hydrogen to flow through the defective hydrogen seal into the bearing compartment and to pass from there into the machine hall through the labyrinth seal. This cannot be prevented by the bleed pump, which conveys only a relatively low volume per time unit. It is true that hydrogen can be prevented from escaping into the power house omission by means of sealing air in the outer labyrinth seal, but this measure is relatively expensive.
A device for safeguarding generators cooled by means of hydrogen gas in the event of the occurrence of impermissible operating states is likewise specified in DE-B 1 038 173. The device has a quick-opening valve, provided directly on the generator housing, of large nominal diameter by means of which an exhaust line leading into the open is opened in the case of danger. The quick-opening valve is a solenoid valve or a valve actuated by a solenoid valve. The solenoid valve is tripped by the operation of a gas pressure switch which is installed in the shaft bearing compartments or in the housing of the generator. Tripping is performed in the case of an increased hydrogen concentration in the shaft bearing compartments.
The article entitled "Erfahrungen mit wasser-stoffgekuhlten Turbogeneratoren" ["Experience with hydrogen-cooled Turbogenerators"] by Franz Bothur in "Elektrizitatswirtschaft", Issue 23, pages 877 to 881, December 1991 describes a hydrogen-cooled generator having an oil seal. The oil seal has an oil outlet chamber to which there is connected an exhaust line which leads into the free atmosphere, but which does not prevent a large quantity of oil from coming into contact with hydrogen and being enriched thereby. Consequently, for generators having higher hydrogen pressures, there is provided as an additional safety measure a pressure-relieving device which opens immediately before the lifting of the shaft seal and discharges most of the hydrogen into the open. The pressure-relieving device is an electromagnetically actuated valve with a large is opening cross-section.